Process for synthesizing specific complete mixed polyol esters

ABSTRACT

Reacting a partial polyol monocarboxylic acid ester with an acidic anhydride in the presence of a catalytic amount of hydrogen bromide to produce specific complete mixed polyol esters, especially confectioner&#39;s hard butter.

BACKGROUND OF THE INVENTION

This invention relates to a process for synthesizing complete mixedpolyol esters, that is, polyol esters having at least two differentester groups and no hydroxyl groups. More particularly, this inventionrelates to a process for esterifying partial polyol esters with minimalrearrangement of ester groups either by intermolecular or intramolecularacyl group exchange, and to confectioner's hard butter compositionsprepared in such fashion. The term "partial polyol ester" is used hereinto denote a polyol which is partially, that is, incompletely, esterifiedand as a consequence contains at least one hydroxyl group.

The instant process provides mixed polyol esters with specific estergroups substantially all at specific polyol hydroxyl sites. This processis especially useful for providing confectioner's hard buttercompositions from inexpensive raw materials such as lard and palm oil.Such compositions are useful as substitutes for cocoa butter inchocolate candies.

To be useful as a confectioner's butter, a triglyceride shouldoptionally have the following characteristics: it should be brittlesolid up to about 77° F.; it should have a relatively narrow meltingrange; and it should be completely liquid at about 95° F., i.e.,slightly below body temperature. Such melting characteristics contributeglossy coatings, absence of stickiness and favorable volume changesduring confectionery product molding. These unique meltingcharacteristics make confectioner's butters such as cocoa butterdesirable for use in confectionery products, especially chocolates.However, cocoa butter is relatively expensive and must be imported, evenwhen domestic fats which can be used to produce acceptableconfectioner's butters are in plentiful supply at much less than thecost of cocoa butter. For many years, therefore, attempts have been madeto provide from readily available and cheaper fats a product that can beused to replace at least part of the cocoa butter in chocolates andother confectionery products that normally contain cocoa butter.

In this search for alternate confectioner's butters, it has beendetermined that the advantageous physical characteristics of suchbutters are derived from the arrangement of the fatty acid substituentsin their glycerides. Analytical tests have shown that cocoa buttercomprises principally fatty acid triglycerides wherein a majorproportion of the oleoyl substituents on the glycerol molecule are inthe 2-position, e.g., 1-palmitoyl-2-oleoyl-3-stearoyl glycerol, andminor amounts of triglycerides having a different order of substitutionof the palmitoyl, oleoyl and stearoyl groups on the glycerol molecule.Accordingly, palmitoyl-oleoyl-stearoyl triglycerides having a majorproportion of the oleoyl groups in the 2-position of the glycerolmolecule would provide the desired confectioner's hard buttercompositions were such triglycerides readily available.

With some esterification procedures, the synthesis of suchposition-specific triglycerides is impossible since substantial estergroup rearrangement occurs during esterification of specific partialglycerides, the synthesis of which is known in the prior art. Thus,acylation of 1,3-diglycerides with oleic acid and a conventional acidesterification catalyst provides only a minor proportion oftriglycerides having an oleoyl group at the 2-position, where this groupmust occur to provide the desired confectioner's butter.

Feuge, Willich and Guice, the Journal of the American Oil ChemistsSociety, July 1963, pp. 260-264, demonstrate that ester grouprearrangement ordinarily occurs during the esterification of partialglycerides, and, at page 260, point out that hydrochloric, sulfuric andhydrocarbyl sulfonic acids, which are widely used as esterificationcatalysts, cause ester group rearrangement. Accordingly, these acidcatalysts are not suitable for preparing the desired position-specific(i.e., 2-oleoyl) triglycerides for use as a confectioner's butter.Similarly, ester group rearrangement ordinarily occurs duringesterification of partial polyol esters other than glycerides, e.g.,during esterification of partial 1,2-propylene glycol esters.

One known method for synthesizing a synthetic confectioner's butterwhich is similar to cocoa butter comprises reacting a diglyceride havingpalmitoyl and stearoyl groups at the 1- and 3-positions with oleoylchloride; see U.S. Pat. 3,012,890. Furthermore, it is known in the priorart that, in general, acid chlorides can be used to specificallyesterify mono- and diglycerides. The use of acid chlorides for specificesterifications has many undesireable aspects, however. For instance,acid chlorides are very corrosive and their use involves handlingproblems.

U.S. Pats. 3,410,881 and 3,337,596 disclose the use of perchloric acidas an effective catalyst for preparing a synthetic cocoa butter withoutrearrangement of the ester groups. However, perchloric acid is known tobe explosive and its use in the presence of organic compounds ispreferably avoided.

The copending application of Yetter, entitled "Process for SynthesizingComplete Mixed Polyol Esters," Ser. No. 242,139, filed Apr. 7, 1972,discloses the use of perfluoroalkyl sulfonic acid catalysts inposition-specific triglyceride syntheses. While effective for theintended use, such perfluorinated catalysts are quite expensive and arein relatively short supply.

The concurrently filed application of O'Connor & Wyness, entitled"Process for Synthesizing Complete Mixed Polyol Esters," Ser. No.279,574, filed Aug. 10, 1972, discloses the use of a non-protonic acidcatalyst, BF₃, as a position-specific esterification catalyst. Whileeffective for the intended use, BF₃ is relatively expensive for use inthe large scale production of triglycerides.

It has now been found that hydrogen bromide catalyzes the esterificationof partial polyol esters without substantial ester group rearrangement.It is surprising that this particular protonic acid catalyzesesterification reactions with only minimal ester group rearrangement,inasmuch as the previously noted Feuge et al., article teaches that ahydrochloric acid esterification catalyst causes complete ester grouprearrangement.

It is therefore an object of this invention to provide a process forsynthesizing complete mixed polyol esters, especially triglycerides,with relatively little rearrangement of ester groups either byintermolecular or intramolecular exchange. It is a further object hereinto provide a process for synthesizing specific complete mixed polyolesters without using perchloric acid, acid chlorides or perfluoroalkylsulfonic acids. Yet another object of this invention is to provide aprocess for the preparation of a confectioner's hard butter composition.These and other objects are obtained herein as will be seen from thefollowing disclosure.

SUMMARY OF THE INVENTION

According to this invention, it has been found that specific completemixed polyol esters, i.e., those with specific ester groups at specificpolyol hydroxyl sites, can be prepared by esterifying partial polyolesters with acid anhydrides in the presence of a catalytic amount of ahydrogen bromide source at temperatures from about -30° F. to about 350°F.

DETAILED DESCRIPTION OF THE INVENTION

Various sources of the hydrogen bromide esterification catalyst used inthe instant process are available, and all such sources are usefulherein. For example, the HBr can be introduced into the reaction mixtureas a gas; or, the HBr can be dissolved in a variety of organic solventsand admixed with the reaction mixture. Alternatively, an aqueoussolution of hydrogen bromide, i.e., the hydrobromic acid of commerce,can be employed. Hydrogen bromide sources based on in situ generation ofHBr, e.g., by the reaction of PBr₃ or SiBr₄ with water, can also beemployed. The most preferred hydrogen bromide sources in the instantprocess are gaseous HBr and aqueous solutions of HBr.

The partial polyol esters to be esterified in the manner of thisinvention are derived from polyols selected from the group consisting of(1) aliphatic diols where the hydroxyl groups are unsymmetricallysubstituted with respect to the carbon chain, or (2) aliphatic polyolscontaining at least three hydroxyl groups. These diols and polyols arepreferably those esterified with acyl substituents derived frommonocarboxylic acids containing from 8 to 24 carbon atoms, although theesterification reaction herein is independent of this chain length.

Partial polyol esters derived from aliphatic diols include for example,esters derived from 1,2-propylene glycol, 1,2-butanediol and1,3-butanediol. Partial polyol esters derived from aliphatic polyolscontaining at least three hydroxyl groups include, for example, estersderived from glycerin, 1,2,4-butanetriol, erythritol, arabitol, xylitol,1,2,6-hexanetriol, sorbitol and mannitol. The ester groups of thesepartial polyol esters include, for example, those derived from caprylic,capric, lauric, myristic, palmitic, stearic, oleic, linoleic, linolenic,arachidic and behenic acids.

Partial polyol esters which are preferred for use herein are partialglyceride esters including 1- and 2-monoglycerides and 1,2- and1,3-diglycerides. The monoglyceride ester groups can be saturated orunsaturated. The diglycerides include disaturated, monoaciddiglycerides, e.g., distearin; disaturated, diacid diglycerides, e.g.,1-palmitoyl - 3 - stearoyl glycerol; diunsaturated, monoaciddiglycerides, e.g., diolein; diunsaturated, diacid diglycerides, e.g.,1-oleoyl-3-palmitoleoyl glycerol; and monounsaturated, monosaturated,diacid diglycerides, e.g., 1-palmitoyl-3-palmitoleoyl glycerol. theterms "diacid" and "monoacid" are used herein to denote glycerideshaving two different acyl substituents and one kind of acyl substituentrespectively. The preparation of partial polyol esters for use in theinstant process is fully described in Mattson and Volpenhein, Journal ofLipid Research, July 1962, vol. 3, No. 3, pages 281-296.

Specific partial carboxylic acid esters of 1,2-propylene glycol can alsobe used in the present process. Most 1-mono-fatty acid esters of1,2-propylene glycol, such as 1-propylene glycol mono-stearate, can beprepared by reacting 1,2-propylene glycol with a desired fatty acid,such as stearic acid, in the presence of a catalyst, such asp-toluenesulfonic acid, and in a solvent, such as xylene, and the1-fatty acid ester separated by fractional crystallization, forinstance, 2-mono-fatty acid esters of 1,2-propylene glycol, such as2-propylene glycol monobehenate, can be prepared by acylation of anappropriately blocked 1,2-propylene glycol derivative, such as1-tetrahydropyranyl propylene glycol, with an acid chloride, such asbehenoyl chloride, and cleavage of the blocking group in the presence ofboric acid.

The symmetrical acidic lipid anhydrides which are preferred for use inesterifying the above partial polyol esters have the structural formula:##EQU1## wherein each X is a substituent selected from the groupconsisting of: (1) alkyl and alkenyl groups containing from 7 to 23carbon atoms and having the formula

    R--

(2) residues of alkyl and alkylene half-esters of a dicarboxylic acidhaving the formula ##EQU2## (3) residues of monoacyl diol half-esters ofa dicarboxylic acid having the formula ##EQU3## (4) residues of diacylglyceride half-esters of a dicarboxylic acid having the formula ##EQU4##and (5) residues of monoacyl derivatives of a primary monohydroxymonocarboxylic acid having the formula ##EQU5## wherein in (1)-(5)above: R is an alkyl or alkenyl group having 7 to 23 carbon atoms; R¹ isan alkylene group having 2 to 4 4 carbon atoms;

R² is an alkylene group having 1 to 4 carbon atoms or hydrogen;

R³ is an alkylene group having 2 to 5 carbon atoms; and

Z is a substituent selected from the group consisting of hydrogen andmethyl.

Another class of acid anhydrides suitable for use in the instant processare those of the formula ##EQU6## wherein R is selected from the groupconsisting of alkyl and alkenyl substituents having from 7 to 23 carbonatoms and Y is selected from the group consisting of benzoyl,p-nitrobenzoyl and alkyl phosphoryl substituents of the formula ##EQU7##wherein R⁴ is a C₁ to C₅ alkyl or phenyl substituent. Theseunsymmetrical acid anhydrides are fully described in U.S. Pat.3,337,596, incorporated herein by reference.

The acid lipid anhydrides in the present process can be prepared inwell-known fashion by admixing the corresponding acidic lipid with anexcess of acetic or propionic anhydride, cooling the reaction product,crystallizing the acid lipid anhydride and collecting the desiredproduct by filtration. The unsymmetrical anhydrides are prepared asdescribed in U.S. Pat. 3,337,596.

The most effective processes for the formation of acidic lipidanhydrides useful in this invention employ metathesis with aceticanhydride either at low temperatures, i.e., 32° F. to 140° F., withperchloric acid catalysis, or at higher temperature, i.e., 140° F. to300° F., without perchloric acid catalysis, but with evaporation of theacetic acid formed in the reaction. See U.S. Pats. 2,163,013 and2,411,567.

Acidic lipids for use in preparing the acidic lipid anhydrides by theabove methods can be derived from a variety of sources, depending on thespecific acidic lipid involved. The acidic lipids for use herein includealiphatic monocarboxylic acids, alkyl half-esters of dicarboxylic acids,monoacyl diol half-esters of dicarboxylic acids, diacyl glyceridehalf-esters of dicarboxylic acids, and monoacyl derivatives of primarymonohydroxy monocarboxylic acids.

The monocarboxylic acids contain from 8 to 24 carbon atoms and include,for example, stearic and oleic acids. They can be readily obtained fromglycerides by saponification, acidulation and isolation procedures or byhydrolysis. The acid desired determines the choice of glyceridicmaterial. For example, a technical grade of stearic acid can be obtainedfrom hydrogenated soybean oil and a technical grade of oleic acid can beobtained from olive oil.

The alkyl half-esters of dicarboxylic acids are condensation products ofdicarboxylic acids having from 4 to 6 carbon atoms with straight chainfatty alcohols containing 8 to 22 carbon atoms. Useful dicarboxylicacids include succinic, glutaric and adipic acids. Useful alcoholsinclude, for example, cetyl and octadecyl alcohols. The dicarboxylicaids are advantageously condensed with the fatty alcohols in a mutualsolvent such as dimethylformamide, dimethylacetamide, dioxane, xylene ortoluene, either with or without the use of a catalyst such as sulfuricacid, p-toluenesulfonic acid, hydrogen chloride, zinc chloride, andother such catalysts. These preparations are best carried out withreaction temperatures in the range of from 175° F. to about 350° F. withwater being removed under reduced pressure. The desired condensationproducts are isolated by appropriate distillation, and/or washing,and/or crystallization treatments if such treatments are required toremove solvents, excess reactants and impurities.

The monoacyl diol half-esters of dicarboxylic acids are the reactionproducts of monoacyl diols and dicarboxylic acid anhydrides. The diolsfor use in preparing these lipids contain from 2 to 6 carbon atoms andcan contain either primary or secondary hydroxy groups. Useful diolsinclude, for example, ethylene glycol, 1,2-propylene glycol,1,3-propanediol, 1,4-butanediol, 1,3-butanediol and 1,5-pentanediol. Anexcess of one of these diols is condensed with a straight chainmonocarboxylic acid, containing 8 to 24 carbon atoms, such as stearic oroleic acid, in the presence of an esterification catalyst, such assulfuric acid, and preferably with refluxing with xylene. Thiscondensation reaction yields a monoacyl diol which in turn is reacted ata temperature ranging from 175° F. to 350° F. with the anhydride of adicarboxylic acid containing 4 to 6 carbon atoms such as succinic,glutaric and adipic acids, to form the desired lipid.

the diacyl glyceride half-esters of a dicarboxylic acid are reactionproducts of diacyl glycerides and dicarboxylic acid anhydrides. Thediacyl glycerides for use in preparing these lipids contain acyl groupsderived from straight chain monocarboxylic acids containing from 8 to 22carbon atoms, such as stearic and oleic acids, and can be prepared asdescribed in the previously referred to Mattson and Volpenheinreference. These diacyl glycerides are reacted at a temperature rangingfrom 175° F. to 350° F. with the anhydride of a dicarboxylic acidcontaining from 4 to 6 carbon atoms, such as succinic, glutaric andadipic acids, to form the desired lipids.

The monoacyl derivatives of a primary monohydroxy-monocarboxylic acidare reaction products of monocarboxylic acid chlorides containing from 8to 24 carbon atoms, such as stearic and oleic acid chlorides, withprimary monohydroxy-monocarboxylic acids having from 3 to 6 carbonatoms. Suitable monohydroxy-monocarboxylic acids include hydracrylic,4-hydroxybutyric, 5-hydroxypentanoic, and 6-hydroxyhexanoic acids. Thedesired lipids can be prepared from these acid chlorides andmonohydroxy-monocarboxylic acids as described in U.S. Pat. 2,251,695.

The unsymmetrical anhydrides useful herein are prepared by reacting thetriethylammonium salt of one acid with the acid halide of the other acidin the manner fully described in U.S. Pat. 3,337,596.

As previously explained, the above partial polyol esters are reactedwith the above acidic lipid anhydrides at a 1:1 mole ratio in thepresence of a hydrogen bromide source. In a preferred mode, an excess ofthe acidic lipid anhydride is employed over that required by thestoichiometry of the reaction; a 10% to 100% molar excess is preferred.The maximum amount of excess lipid anhydride is not critical and molarexcesses of 10 to 20 times can be employed, particularly when theanhydride is being used as the reaction solvent, as noted below. Themolar ratio of hydrogen bromide catalyst to acid lipid anhydride shouldbe at least about 0.01:1; a ratio range of 0.1:1 to 1:1 is preferred forthis molar ratio, but higher ratios are operable.

The position-specific esterification reaction of this invention takesplace over a wide range of temperatures and in the presence of a widevariety of solvents without ester group rearrangement. Reactiontemperatures can range from -30° F. to 350° F., with 0° F. to 212° F.being preferred. The reaction can in most cases be carried out at roomtemperature (ca. 70° F.). It is noted that the reaction normally occursat room temperature in a time period ranging from less than one minuteto five hours. Thus, the reaction of this invention is very rapid whencompared with esterification with acid chlorides, which at roomtemperature normally takes from 10 hours to 24 hours for substantialreaction completeness.

In general, the reaction solvent herein, if any, can be any organicliquid medium which will form a phase sufficiently uniform so as tobring the reactants into contact. Preferably, if it is a liquid, a molarexcess of the acid lipid anhydride is used as the solvent, this excessbeing calculated on the basis of only one acidic lipid group of eachanhydride molecule reacting. Other useful solvents include chlorinatedhydrocarbons such as chloroform and carbon tetrachloride, aromatichydrocarbons such as benzene and aliphatic esters such as ethyl acetate.Still other useful solvents include aromatic heterocyclic bases such aspyridine, tertiary amides such as dimethylformamide anddimethylacetamide, heterocyclic oxides such as tetrahydrofuran, andfatty acids.

In the case where monoglycerides are the partial polyol esters, thespecific solvent used seems to have some effect on whether substantiallyno ester group rearrangement occurs; benzene and pyridine are desirablyused as solvents in this case.

Turning now to one specific application of the above described generalprocess, that is, a process for preparing a confectioner's hard butter,it has been found that certain 1,3-diglycerides can be esterified witholeic acid anhydride by the above described general method to providehard butter compositions. This process is illustrated by the followingequation: ##EQU8##

Although the stoichiometry of the reaction indicates that, at a 1:1molar ratio of acid anhydride:polyol, two moles of acid are present, thesecond mole of acid is not involved in the esterification since it isnot in the anhydride form. Of course, anhydride:polyol mole ratios ofless than 1:1 can be used herein, but this results in proportionateamounts of unesterified polyol in the product.

The 1,3-diglycerides used in this process can be obtained bysuperglycerination of lard or of substantially completely hydrogenatedpalm oil in the presence of triacetin using the method of Baur andLange, Journal of the American Chemical Society, 1951, vol. 73, page3926. Alternatively, the glycerolysis of hydrogenated palm oil using analkoxide catalyst can be used (see U.S. Pat. 2,442,534).

The following example illustrates the preparation of a confectioner'sbutter useful as a synthetic cocoa butter in greater detail but is notto be construed in any way as limiting the scope of the invention.Unless otherwise specified, all percentages in the following examplesare by weight.

EXAMPLE I Preparation of a confectioner's hard butter

Following the procedure set forth in U.S. Pat. 2,442,534, 1.6 g. ofsodium methoxide is reacted with 16 g. of glycerin for one-half hour atroom temperature, under vacuum (to remove methanol). Three hundred andfour grams of palm oil hydrogenated to an iodine value of 8 and havingan acid value of 0 are reacted continuously with the foregoing mixtureof glycerin and sodium methoxide at about 250° F. for 10 minutes. Atthis point, excess sodium methoxide is neutralized with H₃ PO₄. Excessglycerin is removed by vacuum stripping and the mixture is filtered. Thereaction mixture is extracted using countercurrent streams of wetmethanol and n-hexane. The hexane stream is recovered and chilled to ca.60° F. to crystallize the desired 1,3-diglycerides.

Optionally, the solidified 1,3-diglycerides can be further purified asfollows: the solid mass from the hexane extract is slurried with 30 ml.of aqueous acetic acid solution containing 50% water by volume. Theslurry is dissolved in 4 liters of ethanol-hexane solution (50% ethanolby volume) and the resulting solution cooled to 50° F. This temperatureis maintained for about a four-hour period, during which time crystalsare formed. At the end of the four-hour period, the crystals areseparated by vacuum filtration and recrystallized overnight from 3liters of ethanol-hexane solution (50% ethanol by volume). The crystalsrecovered by filtration are dissolved in one liter of ethyl ether andwater-washed three times. The ether is removed by evaporation and theresidue crystallized from 2.5 liters of ethanol-hexane solution (50%ethanol by volume) at 50° F. After filtration the crystals are air driedto provide the substantially pure product.

Analysis of the above product shows it to be substantially all1,3-diglyceride containing palmitoyl and stearoyl groups. The aboveproduct has a hydroxyl value of 90-92 as compared with a theoreticalvalue of 94.2 for 100% diglyceride and contains less than 0.5%monoglycerides. It has a complete melting point of 159° F.-160° F.Analysis for specific acid groups shows the presence of ca. 35% palmiticand ca. 65% stearic, and minor amounts of myristic, all by weight witheach acid group expressed as the corresponding acid.

Oleic anhydride is prepared by refluxing 100 grams of oleic acid in 300grams of acetic anhydride for three hours. The bulk of the distillablematerial present, mostly acetic acid, is then removed at atmosphericpressure. The residue is then heated at 355° F. under 1 to 2 mm. Hgpressure for 30 minutes to distill the remaining volatile impurities.

Sixty-one grams of the 1,3-diglyceride mixture prepared in the foregoingmanner and comprising about 45% 1-palmitoyl-3-stearoyl glycerol, 42% 1,3distearoyl glycerol, about 11% 1,3 dipalmitoyl glycerol, the balancebeing mixed 1,3 diglycerides, were admixed with 250 grams of a 1:1mixture of oleic acid and oleic anhydride prepared as described above.One ml. of aqueous 65% hydrobromic acid was added to the mixture and thereactants stirred together at room tempeature for one and one-halfhours. An equal volume of water was added to the reaction mixture, whichwas then heated to 180° F. for 30 minutes to hydrolyze excess oleicanhydride. The water was removed and discarded and the residue extractedfive times with equal volumes of methanol to remove traces of free acid.

Analysis of the triglyceride product by thin layer chromatography showedthat it contained about 90% triglyceride, less than 2% unreacteddiglyceride and about 1% free fatty acid. Analysis by argenationchromatography showed that it contained 55%-60% by weight of oleic acidesterified at the 2-position, indicating that a significantly reducedlevel of ester group rearrangement occurs in this process.

Further similarity between the above 2-oleoyl triglyceride compositionand a commercially-available cocoa butter is shown by a comparison ofconsistencies as follows. Samples of the above-prepared triglyceride andcommercially-available cocoa butter are melted; chilled in ice for fiveminutes; held for one day at 70° F.; held for one week at 80° F.; andheld overnight at 50° F.; and the solids content at these varioustemperatures determined at the end of the period by the dilatomericmethod described in Fulton, Lutton and Willie, Journal of the AmericanOil Chemists Society, March 1954, vol. XXXI, No. 3, pp. 98-103.Comparison of the "melting" curves for the synthetic triglyceride andfor the commercially-available cocoa butter shows that both of theseproducts have similar consistencies over the range of temperatures fromabout 70° F. to about 95° F., i.e., that range of temperatures overwhich cocoa butter has its unique melting characteristics.

In summary, the above synthetic triglyceride has substantially similarweight proportions and distribution of fatty acids and substantiallyequivalent consistency characteristics to a commercially-available cocoabutter.

In the above procedure, the 48% aqueous hydrobromic acid is replaced byan equivalent amount of 30% ethanolic solution of HBr; in an alternateprocedure, gaseous HBr is bubbled through the reaction mixture at a rateof about 0.01 mole/hour during the course of the reaction between theoleic anhydride and 1,3-diglyceride mixture. In each instance,equivalent results are secured in that a confectioner's butter similarto cocoa butter is secured with little ester rearrangement.

The above procedure is carried out in a solvent amount of dry chloroformwith equivalent results.

The above procedure is carried out at 0° F. and 212° F. (pressurevessel), respectively, and equivalent results are obtained.

In the above procedure, the oleic anhydride is replaced by an equivalentamount of oleic-benzoic anhydride, oleic-p-nitrobenzoic anhydride andoleic-ethylphosphoryl anhydride, respectively, and synthetic 2-oleoyltriglycerides suitable for use as a cocoa butter substitute are securedin each instance.

The above procedure is carried out using mole ratios of hydrogenbromide-to-acidic lipid anhydride of 0.01:1 and 0.5:1 with equivalentresults.

The above procedure is carried out using the saturated 1,3-diglyceridesobtained from superglycerinated lard and an equivalent syntheticconfectioner's hard butter is secured.

EXAMPLE II Esterification of 1,3-dipalmitin with oleic anhydride

Twenty grams of 1,3-dipalmitin made as described in Example 2 of U.S.Pat. 2,626,952 and 30 ml. of oleic anhydride made as in Example I hereinare admixed in 50 ml. of water-washed, distilled and dried chloroform inthe presence of 0.05 mole of hydrogen bromide (as ethanolic HBr). Thereactants are stirred at room temperature for three hours.

The reaction mixture is dissolved in 500 ml. ethyl ether together with100 ml. water. The ether phase is water-washed three times, dried andevaporated in an inert atmosphere. The residue is crystallized twicefrom acetone at 20° F. and the crystals dried to provide substantiallypure triglyceride product.

The product has an acid value of ca. 0.8 and a hydroxyl value of 2.0,showing that substantially all the product is triglyceride. The2-position fatty acids are isolated by the pancreatic enzyme procedureof Mattson and Volpenhein, J. Lipid Research, January 1962, No. 2, pp.58-64, and the triglyceride is found to contain about 80-85% by weightoleic acid at the 2-position, i.e., 1-palmitoyl-2-oleoyl-3-palmitoylglycerol, demonstrating that substantially no existing ester grouprearrangement occurs during the above esterification reaction.

In the above procedure the 1,3-dipalmitin is replaced by an equivalentamount of 1,3-distearoyl glycerol, 1-palmitoyl-3-stearoyl glycerol,1-palmitoyl-3-lauroyl glycerol and 1-behenoyl-3-stearoyl glycerol,respectively, and the corresponding 2-oleoyltriglycerides are formedwithout substantial ester group migration.

In the above procedure the chloroform is replaced by an equivalentamount of carbon tetrachloride, benzene and hexane, respectively, andequivalent results are secured.

The above procedure is repeated using an equivalent amount of1,2-dipalmitin as the partial glyceride and 1-oleoyldipalmitin issecured, demonstrating that essentially no ester group rearrangementoccurs with the hydrogen bromide catalyst herein.

EXAMPLE III Esterification of 1,3-dipalmitin with rapeseed oil fattyacid anhydride

Rapeseed oil fatty acid anhydride is formed as follows: rapeseed oil ishydrolyzed to the corresponding rapeseed oil fatty acids. These fattyacids are formed into the corresponding long chain fatty acid anhydridesby the anhydride-forming process disclosed in Example I. The anhydridesso formed are for the most part mixed anhydrides, that is, eachanhydride molecule contains two different fatty acid groups. Theseanhydrides react in the same manner as if each molecule contains twoidentical fatty acid groups.

Two grams of rapeseed oil fatty acid anhydride, 1.5 grams of1,3-dipalmitin prepared as in Example II, 10 ml. purified chloroform and0.025 ml. 15% aqueous hydrobromic acid are reacted together withvigorous mixing at room temperature (ca. 70° F.) for one hour. Thereaction product is diluted with 100 ml. ethyl ether, water-washed andthe solvent evaporated in an inert atmosphere. The residue iscrystallized three times from 75 ml. acetone at 20° F. to provide thepurified product.

Thin layer chromatography shows that substantially all the product istriglyceride. Analysis of the triglyceride by argentation chromatographyand comparison of the 2-position fatty acid composition of thetriglyceride with the original rapeseed oil fatty acids indicate thatthe palmitic, stearic, oleic, palmitoleic, linoleic, linolenic anderucic acid fractions of the rapeseed oil each esterify the1,3-dipalmitin primarily at the 2-position.

EXAMPLE IV Esterification of 2-monostearin

One-half gram of 2-monostearin made by the process described in Martin,Journal of the American Chemical Society, 1953, voln. 75, p. 5482, 1.84grams oleic anhydride made as in Example I, 10 ml. benzene and 0.01 ml.48% aqueous hydrobromic acid are reacted together with mixing at 70° F.for three hours.

The reaction mixture is diluted with ethyl ether, water-washed and thesolvent removed by evaporation. The residue is crystallized twice from20 ml. acetone at 20° F. The major portion of the product is2-stearoyldiolein; therefore, substantially no existing ester grouprearrangement occurs during the esterification reactions.

In the above procedure, the benzene solvent is replaced with anequivalent amount of pyridine with equivalent results.

In the above procedure the aqueous hydrobromic acid is replaced by anequivalent amount of a 1:3 (molar basis) mixture of PBr₃ and H₂ O, andby a 30% (wt.) methanol solution of HBr, respectively, and equivalentresults are secured.

EXAMPLE V Esterification of 1-monostearin with stearoyl propylene glycolsuccinate anhydride

Forty-four grams (0.1 mole) of stearoyl propylene glycol hydrogensuccinate are mixed with 30 grams (0.3 mole) of acetic anhydride andheated at reflux for one hour. The mixture is then heated at 250° F. to265° F. for two hours under a pressure of 2-5 mm. Hg. The residue iscooled with recovery of about a 96% yield of stearoyl propylene glycolsuccinate anhydride (an anhydride having the previously describedstructural formula wherein X is a residue of a monoacyl diol half-esterof a dicarboxylic acid).

Three and six-tenths grams of 1-monostearin (0.01 mole) prepared by theprocess described in Mattson and Volpenhein, Journal of Lipid Research,July 1962, vol. 3, No. 3, pp. 283, 284, are dissolved in 144 ml. benzenewith slight warming. Nineteen grams (0.022 mole) of the above preparedstearoyl propylene glycol succinate anhydride are added with stirring.The sample is treated with 0.1 ml. of 48% aqueous hydrogen bromidecatalyst and stirring continued at 90° F. for one hour.

The reaction mixture is diluted with 100 ml. water and the mixtureshaken in a separatory funnel. The washed benzene solution is dried andthe product isolated by chromatography on a 300 gram silica gel (+ 5%water) column. Elution with one liter of benzene and with one liter ofbenzene containing 2% ethyl ether and 1% acetic acid yields about 11grams of product. Fractional crystallization of the product from 15volumes of acetone at 70° F., 50° F. and 0° F. provides a productcomprising about 80% 1-stearoyl-2,3-di(stearoyl propylene glycolsuccinyl) glycerol having the structural formula ##EQU9## Substantiallyno existing ester group rearrangement occurs during the aboveesterification reaction.

EXAMPLE VI Esterification of 1,3-distearin with octadecyl glutarateanhydride

Octadeyl glutarate anhydride (an anhydride having the previouslydescribed structural formula wherein X is a residue of an alkylhalf-ester of a dicarboxylic acid) is prepared the same as the anhydridein Example V but with substitution of a molar equivalent of octadecylhydrogen glutarate for the stearoyl propylene glycol hydrogen succinate.

Six and two-tenths grams distearin prepared as in Example I of U.S. Pat.2,626,952 are dissolved in 120 ml. benzene with stirring and slightwarming. Seven and nine-tenths grams of the above octadecyl glutarateanhydride are added; when the reagents are completely dissolved, 0.001mole of gaseous HBr is introduced below the surface of the reactionmixture. The mixture is then stirred at room temperature for one hour.

The reaction mixture is diluted with 100 ml. water and the aqueous layerseparated and discarded. The benzene layer is washed twice with water,dried with five grams sodium sulfate, filtered and evaporated todryness. The residue is crystallized from 200 ml. acetone at 195° F. Thecrystals are recrystallized from 150 ml. acetone at 212° F. to provide1,3 - distearoyl - 2 -octadecyl glutaryl glycerol. Substantially noexisting ester group rearrangement occurs during the aboveesterification reaction.

EXAMPLE VII Esterification of 1,3-distearin with1,3-distearin-2-succinate anhydride

1,3 - distearin - 2 - succinate anhydride (an anhydride having thepreviously described structural formula wherein X is a residue of adiacyl glyceride half-ester of a dicarboxylic acid) is prepared in thesame manner as the anhydride in Example V but with substitution of amolar equivalent of 1,3-distearin-2-hydrogen succinate for the stearoylpropylene glycol hydrogen succinate.

Six and two-tenths grams 1,3-distearin are dissolved in 250 ml. benzenewith stirring and slight warming. Fifteen grams of the above1,3-distearin-2-succinate anhydride are added and dissolved withstirring. When the reagents are completely dissolved, 0.2 ml. ofconstant boiling (1 atm.) aqueous hydrobromic acid is added and thereaction mixture stirred at 100° F. for one hour.

In order to purify the product, 100 ml. water are added and the aqueousphase separated and discarded. The product is further purified bytreatment with three 30-gram portions of base-form ion exchange resin.The benzene solution is evaporated and the residue crystallized from 200ml. acetone at 90° F. to provide di(1,3-distearin)succinate.Substantially no existing ester group rearrangement occurs during theabove esterification reaction.

The above process is carried out at 0° F., 30° F. and 200° F.,respectively, with equivalent results.

EXAMPLE VIII Esterification of propylene glycol monooleate withstearoyl-4-hydroxybutyric anhydride

One mole 1,2-propylene glycol is reacted with 0.5 mole oleic acid in oneliter of xylene in the presence of 0.01 mole of p-toluene sulfonic acidcatalyst. The sample is refluxed under a moisture trap for two hours,poured into ice water, water-washed and the solvent evaporated toprovide 70% pure propylene glycol monooleate. The impure product ispurified with a silica gel column to provide about 0.35 mole ofsubstantially pure propylene glycol monooleate. The propylene glycolmonooleate is present as a mixture of isomeric esters with about 80% ofthe oleoyl groups at the primary hydroxyl position and 20% at thesecondary position of 1,2-propylene glycol.

Stearoyl - 4 - hydroxybutyric anhydride (an anhydride having thepreviously described structural formula wherein X is a residue of amonoacyl derivative of a primary monohydroxy monocarboxylic acid) isprepared the same as the anhydride in Example V but with substitution ofa molar equivalent of stearoyl - 4 - hydroxybutyric acid for thestearoyl propylene glycol hydrogen succinate.

Three and four-tenths grams of the above propylene glycol monooleate aredissolved in 100 ml. benzene. Ten grams of the above stearoyl - 4 -hydroxybutyric anhydride are added to the solution and stirred withslight warming until dissolution is complete. When the reagents arecompletely dissolved, 0.1 ml. 47% hydrobromic acid is added and stirringcontinued at 70° F. for one hour.

In order to purify the desired product, the reaction mixture is dilutedwith 100 ml. water and the aqueous phase is separated and discarded. Thebenzene layer is evaporated to dryness and the residue is dissolved in100 ml. hexane. The hexane solution is crystallized at 50° F. to yieldprimarily stearoyl - 4 - hydroxybutyric acid. The filtrate from the 50°F. crystallization is evaporated to dryness and this residue isdissolved in 200 ml. acetone. The acetone solution on crystallization at40° F. provides oleoyl (stearoyl - 4 - hydroxybutyryl) propylene glycol.The product consists of a mixture of isomeric esters with ca. 60% byweight of the oleoyl groups at the primary hydroxyl position and 40% atthe secondary hydroxyl position of 1,2-propylene glycol. This mixture ofisomers partially results from the fact that the propylene glycolmonooleate used consists of an 80-20 mixture of primary and secondaryesters respectively. Thus, very little existing ester grouprearrangement occurs during the above esterification reaction.

EXAMPLE IX Esterification of 1-propylene glycol monobehenate with oleicanhydride

1-propylene glycol monobehenate is made as follows: ethyl lactate (450grams, 3.8 moles) is mixed with 1.2 ml. concentrated hdyrochloric acidand the mixture cooled in an ice bath. Dihydropyran (420 grams, 4.9moles) is added with stirring, after which the sample is allowed to warmto room temperature. After three hours, 10 grams of potassium carbonateare added and the sample stirred. The product is distilled under reducedpressure with collection of 366 grams tetrahydropyranyl ethyl lactateboiling at 65° to 70° C. at 1-2 mm. pressure. Tetrahydropyranyl ethyllactate (82 grams, 0.46 mole) is dissolved in 300 ml. tetrahydrofuranand the solution is cooled in an acetone-ethanol Dry Ice bath. The THPethyl lactate solution is added slowly to a 10% lithium aluminum hydridesolution and subsequently the mixture is warmed to room temperature. Thereactants are diluted with 150 ml. ethanol, followed by two liters ofwater. The sample is then extracted three times with 400 ml. portions ofbenzene. The benzene extracts are dried with sodium sulfate, filtered,and the filtrate is distilled with collection of the fraction boiling at78-81° C. at 3 mm. pressure. The yield is 28 grams of2-tetrahydropyranyl propylene glycol.

2-tetrahydropyranyl propylene glycol (16.0 grams, 0.1 mole) isinteresterified with 39 grams methyl behenate using 4 ml. of 40%trimethyl benzyl ammonium methoxide as a catalyst. The reactants arestirred in a 250 ml. flask heated at 60-80° C. under a reduced pressureof 200 mm. Hg for 6 hours. The reactants are poured into 600 ml. ofhexane and the hexane solution washed with 400 ml. of 1% potassiumbicarbonate solution. The washed hexane layer is diluted with 200 ml.ethanol and 75 grams urea are added to the sample. Adduct formation withurea is accomplished by stirring the sample initially at 40° C. andallowing the mixture to cool at 25° C. during a two-hour interval. Theurea adduct is removed by filtration and discarded. The adduction withurea is repeated using 60 grams urea. The filtrate from the second ureaadduction is water-washed three times and the hexane layer is evaporatedto dryness. The residue is dissolved in 300 ml. hexane and the solutionis crystallized at -18° C. Filtration at -18° C. yields 21.3 grams of1-behenoyl-2-tetrahydropyranyl propylene glycol.1-behenoyl-2-tetrahydropyronyl propylene glycol (8 grams, 0.0165 mole)is cleaved by reaction with 11 ml. of 1.6 molar boric acid in trimethylborate. The reactants are heated in a boiling water bath withapplication of vacuum. Heating is continued for 15 minutes with a vacuumof 2-5 mm. Hg pressure during the final 10 minutes. The residue iscooled to room temperature and dissolved in 200 ml. ethyl ether andwater-washed three times. The ether phase is dried with sodium sulfate,and evaporated to dryness on an evaporator without warming above 30° C.The residue is dissolved in 100 ml. petroleum ether and crystallized at70° F. The crystals recovered at 70° F. are recyrstallized from 200 ml.petroleum ether at 50° F. to yield ca. 5 grams of 1-propylene glycolmonobehenate.

Five grams of the above prepared 1-propylene glycol monobehenate aredissolved in 100 ml. benzene together with 6 grams oleic anhydride madeas in Example I. The sample is stirred at room temperature untilsolution is complete. One-tenth ml. 60% (wt.) aqueous hydrobromic acidis added and the sample stirred for 30 minutes at room temperature.

In order to purify the product 100 ml. water are added and the aqueousphase separated and discarded. The benzene solution is evaporated todryness and the residue dissolved in 100 ml. acetone. The acetonesolution is crystallized at 0° F. with recovery of ca. 85% pure1-behenoyl-2-oleoyl propylene glycol, indicating that very littleexisting ester group rearrangement occurs during the aboveesterification reaction.

EXAMPLE X Esterification of 1,4-distearoyl erythritol with oleicanhydride

One mole erythritol is reacted with two moles methyl stearate in oneliter of dimethylacetamide in the presence of 0.1 mole sodium methoxidecatalyst. The reaction mixture is heated at 100-120° C. under reducedpressure (80-100 mm. Hg) for three hours with slow distillation ofsolvent such that about 400 ml. of solvent is removed in the three-hourperiod. Twency cc. of 50% by volume aqueous acetic acid are added to thesample and this mixture poured into two liters of water. One liter of anethyl acetatebutanol mixture (four parts by volume ethyl acetate to onepart by volume butanol) is added. The ethyl acetatebutanol layer isseparated, water-washed twice and treated with 500 grams urea. Thismixture is stirred at room temperature for two hours. The mixture isthen filtered and 0.12 mole of 1,4-distearoyl erythritol is recoveredfrom the urea adduct by dissolving in acetone and crystallizing at 90°F.

Six and one-half grams of the above 1,4-distearoyl erythritol aredissolved in 200 ml. ethyl acetate with slight warming while stirring.Six and six-tenths grams oleic anhydride prepared as in Example I areadded, followed by 0.1 ml. 48% aqueous hydrobromic acid. The reactionmixture is stirred at room temperature for one hour.

In order to purify the product, the reaction mixture is washed theretimes with water and the ethyl acetate solution dried with 15 grams ofsodium sulfate and filtered. The solution after crystallizing 24 hoursyields substantially pure 1,4-distearoyl-2, 3-dioleoyl erythritol.Substantially no existing ester group rearrangement occurs during theabove esterification reaction.

The foregoing examples illustrate the use of hydrogen bromide sources asthe catalyst in the esterification of partial polyol esters with acidlipid anhydrides of various types. The examples are not intended to belimiting of the types of acid anhydrides and types of partial polyolesters useful in the process of this invention.

As will be seen from the following example, carboxylic acid anhydrideshaving hydrocarbyl substituents from 1 to about 30 carbon atoms and arylsubstituents such as phenyl, tolyl, xylyl, naphthyl and the like, arealso suitably employed in conjunction with partial polyol esters of alltypes to provide position-specific esterification reactions.Furthermore, the partial polyol esters useful herein are not limited intheir type and can contain ester groups having from 1 to about 30 carbonatoms, and greater. It is to be understood, therefore, that theposition-specific esterification reaction herein appears to be a generalone in that it provides for the esterification of all manner of partialpolyol esters by means of all manner of organic acid anhydrides withoutsubstantial ester group rearrangement.

EXAMPLE XI Esterification of 1,3-dipropanoyl glycerol with aceticanhydride

One mole of 1,3-dipropanoyl glycerol is admixed with two moles of aceticanhydride and dissolved therein with heating and stirring at atemperature of about 175° F. A volume of 48% (wt.) aqueous hydrobromicacid sufficient to provide 0.5 mole of HBr is admixed with the reactionsolution and the temperature is restored to room temperature (70° F.)over a two hour period. The reaction mixture is poured into 1 liter ofwater which serves to hydrolyze the unreacted acetic anhydride.

Excess water is removed by vacuum evaporation at about 90° F. on arotary evaporator, which process also removes much of the acetic acid.The residue left after evaporation is dissolved in a 1:1 mixture ofethyl alcohol and benzene and a 1.0 M solution of barium chloride isadded thereto, protionwise, until precipitation of the insoluble bariumacetate mono-hydrate is complete. The solids are removed by filtrationand the benzene-alcohol solvent is removed on the rotary evaporatorunder vacuum. The resulting triglyceride product is substantially pure1-propanoyl-2-acetyl-3-propanoyl glycerol, indicating that theesterification occurs without substantial intramolecular orintermolecular acyl group rearrangement.

The above procedure is carried at 0° F. and 212° F., respectively, withsubstantially equivalent results.

The procedure is carried at a catalyst-to-anhydride mole ratio of 0.01:1with equivalent results.

The aqueous hydrobromic acid used in the above process is replaced by anequivalent amount of a benzene solution of HBr, gaseous HBr and anamount of SiBr₄ and H₂ O sufficient to provide 0.5 mole of HBr,respectively, and equivalent resins are secured.

In the above procedure the acetic anhydride is replaced by an equivalentamount of benzoic acid anhydride and the reaction product issubstantially all 1-propanoyl-2-benzoyl - 3 - propanoyl glycerol,indicating that substantially no ester group rearrangement occurs in theprocess.

What is claimed is:
 1. A process for preparing specific complete mixedpolyol esters from .[.unsymmetrically substituted.]. partial polyolesters with substantially no ester group rearrangement comprisingesterifying .[.said.]. .Iadd.a .Iaddend.partial polyol .[.esters.]..Iadd.ester .Iaddend.with an acid anhydride in the presence of acatalytic amount of a hydrogen bromide source.[...]..Iadd., said partialpolyol ester being from the group consisting of partial polyol estersfrom aliphatic diols having the hydroxyl groups unsymmetricallysubstituted with respect to the carbon chain and partial polyol estersfrom aliphatic polyol containing at least three hydroxyl groups..Iaddend.
 2. A process according to claim 1 wherein the hydrogen bromidesource is selected from the group consisting of aqueous hydrobromic acidand gaseous hydrogen bromide.
 3. A process according to claim 1comprising admixing: (1) a polyol selected from the group consisting ofaliphatic diols wherein the hydroxyl groups are unsymmetricallysubstituted with respect to the carbon chain and aliphatic polyolscontaining at least three hydroxyl groups, said polyols having beenpartially esterified with a monocarboxylic acid containing about 8 to 24carbon atoms, with; (2) a member selected from the group consisting ofacidic lipid anhydrides of the formula ##EQU10## wherein X is asubstituent selected from the group consisting of:(1) alkyl and alkenylgroups containing from 7 to 23 carbon atoms and having the formula R--(2) residues of alkyl half-esters of a dicarboxylic acid having theformula ##EQU11## (3) residues of monoacyl diol half-esters of adicarboxylic acid having the formula ##EQU12## (4) residues of diacylglyceride half-esters of a dicarboxylic acid having the formula##EQU13## and (5) residues of monoacyl derivatives of a primarymonohydroxy monocarboxylic acid having the formula ##EQU14## wherein in(1)-(5) above: R is an alkyl or alkenyl group containing 7 to 21 carbonatoms; R¹ is an alkylene group containing 2 to 4 carbon atoms; R² is analkylene group containing 0 to 4 carbon atoms; R³ is an alkylene groupcontaining 2 to 5 carbon atoms; Z is a substituent selected from thegroup consisting of hydrogen and methyl; and Y is a substituent selectedfrom the group consisting of benzyl, p-nitrobenzyl, and phosphorylester; and(3) a catalyst selected from the group consisting of hydrogenbromide and hydrogen bromide sources, at a molar ratio of said catalystto acidic lipid anhydride of at least about 0.01 to
 1. 4. The process ofclaim 1 which is carried out at a temperature from 0° F. to 212° F. 5.The process of claim 1 which is carried out using a molar excess of theacid anhydride.
 6. The process of claim 1 wherein the partial polyolester is a partial glyceride ester.
 7. The process of claim 1 whereinthe partial polyol ester is a 1,3-diglyceride.
 8. The process of claim 1wherein the partial polyol ester is a partial ester of 1,2-propyleneglycol.
 9. The process of claim 1 wherein the acid anhydride issymmetrical.
 10. The process of claim 1 wherein the acid anhydride is analkyl anhydride wherein the alkyl group contains from 7 to about 23carbon atoms.
 11. The process of claim 1 wherein the acid anhydride isoleic anhydride.
 12. The process of claim 1 wherein the partial polyolester is a monoglyceride and the reaction is carried out in an organicsolvent selected from the group consisting of benzene and pyridine. 13.A process for preparing a synthetic cocoa butter comprising acylatingthe 2-hydroxy group of 1-palmitoyl-3-stearoyl glycerol with oleicanhydride in the presence of a catalyst selected from the groupconsisting of hydrogen bromide and hydrogen bromide sources, andcrystallizing and separating the synthetic cocoa butter thus formed. 14.A process for preparing a confectioner's hard butter comprisingacylating the 2-hydroxy groups in a mixture comprising1-palmitoyl-3-stearoyl glycerol, 1,3-distearoyl glycerol and1,3-dipalmitoyl glycerol with oleic anhydride in the presence of acatalytic amount of hydrogen bromide.
 15. A process for preparing aconfectioner's hard butter comprising: (1) admixing substantiallycompletely hydrogenated palm oil with glycerol in the presence of asodium methoxide catalyst and separating and crystallizing the1,3-diglycerides formed; (2) acylating the 2-hydroxy groups of the1,3-diglycerides prepared in step (1) with oleic anhydride in thepresence of a catalyst selected from the group consisting of hydrogenbromide and hydrogen bromide sources; and (3) crystallizing andseparating the hard butter thus formed.
 16. The process of claim 15wherein the catalyst is a member selected from the group consisting ofhydrogen bromide gas and aqueous hydrobromic acid.
 17. The process ofclaim 15 wherein the catalyst-to-oleic anhydride molar ratio is at least0.01:1.
 18. The process of claim 15 which is carried out at from about0° F. to about 212° F.
 19. The process of claim 15 which is carried outin the presence of a molar excess of oleic anhydride.